A switch in the cold
We aim to manipulate light to lay the foundation for quantum communication. Our approach involves using active switches to manipulate the fundamental properties of light: phase, polarization, or propagation direction. To manipulate these properties in a compact device, we can utilize the crystal lithium niobate. Applying voltage to this crystal changes its refractive index. Through a carefully chosen geometry of the device, the phase, polarization, and propagation direction of light in the crystal can be manipulated.
These modulators can already operate at room temperature. However, we aim to interconnect multiple optical components for quantum communication. Quantum light sources and highly efficient single-photon detectors mainly function at cryogenic temperatures. Therefore, we also need to be able to operate our modulators at cryogenic temperatures.
Our 3 modulator types
In the material system lithium niobate, we can guide light. To achieve this, we apply titanium strips to the crystals and heat them. Heating causes titanium to diffuse into the crystal, locally increasing the refractive index. As a result, we can guide light with an optical waveguide within the crystal.
To realize our light modulators, we additionally apply gold electrodes to the surface, to which we can apply voltages. Applying voltages alters the refractive index in the waveguide. By choosing the geometry, we can change the phase, propagation direction, or polarization.
Measurements at low temperatures
In our modulators, we are interested in efficiently switching from one state to another. This means, for example, manipulating light from a horizontal to a vertical oscillation with the lowest possible switching voltage. To investigate this at different temperatures, we integrate our modulators into a cryostat. We then couple light into the waveguides of the modulators and apply voltages to the electrodes. We can subsequently record the resulting change in light within the modulator.
Measurement of our modulators shows that we require higher voltages to switch light at cryogenic temperatures compared to room temperature. Additionally, the optimal operating wavelength of the modulator shifts with temperature changes.
In summary, we can efficiently manipulate light with these modulators both at room temperature and at 1K.
Video zum Thema
Wir haben ebenfalls ein Video produziert, dieses ist allerdings nur auf Englisch verfügbar.
Publications on this topic
F. Thiele, F. vom Bruch, V. Quiring, R. Ricken, H. Herrmann, C. Eigner, C. Silberhorn, T. Bartley, Optics Express (2020).
F. Thiele, F. vom Bruch, J. Brockmeier, M. Protte, T. Hummel, R. Ricken, V. Quiring, S. Lengeling, H. Herrmann, C. Eigner, C. Silberhorn, T. Bartley, Journal of Physics: Photonics 4 (2022).
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